Sorry for the really noobie post, but I was hoping someone could point me in a good direction for starting modding with Source, Sin specifically.

I havent done any level designing for years now, the last one I used was Build engine for Duke 3D. Emergence has given me a similar vibe and playstyle that I really love, and I'd love to be able to design my own levels, skins and such again. Anyone know a good place to start from, interesting tutorials etc.